Sheet metal is used to form the basic components of many commercial products. For example, sheet metal is used to form parts for automobiles, appliances, airplanes and other mass produced items. To transform the sheet metal into an appropriately sized and shaped part, the sheet metal is pressed, bent, cut, pierced, trimmed, etc.
A transfer press is typically used to expedite the process of forming parts from sheet metal. Transfer presses typically include several upper and lower die combinations referred to as press stations that are arranged in a line within the transfer press. The dies for each press station are chosen to perform specified functions to create the desired part. Additionally, the transfer press includes an automated system that transfers the parts from one station to the next to increase the rate of output by the transfer press.
Over the years, the size of parts formed from sheet metal have increased significantly. For example, individual parts for automobiles such as doors and body panels have increased in size. The larger parts slow down the transfer press thus decreasing its throughput capability. It simply takes longer to move a large part between the press stations. Additionally, the larger parts make it more difficult to reorient the part between dies because the larger parts are more difficult to handle.
Prior systems and methods for transferring a work piece in a multi-station press have used independent vertical and horizontal movement of a cross bar assembly. This independent vertical and horizontal movement limited the rate at which large work pieces could be processed. Other prior systems used simultaneous vertical and horizontal movement of the cross bar assembly to increase the output rate of the transfer press. This type of movement is shown by way of example in U.S. Pat. No. 5,148,697 issued to Shiraishi, et al. entitled METHOD FOR WITHDRAWING WORK PIECE FROM DRAWING MOLD and U.S. Pat. No. 4,981,031 issued to Schneider, et al. entitled TRANSFER DEVICE IN A TRANSFER PRESS OR SIMILAR METAL-FORMING MACHINE. Shiraishi and Schneider both disclose movement of a cross bar along a curved path from a rest position between stations to a first press station. The part is transplanted from the first press station to a second press station over a curved path and the cross bar returns to the rest position between press stations. The cross bar stays in the rest position during a press operation.
The Schneider patent also shows cross bar assemblies with carriages formed in a low-mass construction. This low-mass construction allows increased acceleration and thus the press may operate at a higher speed. Schneider also discloses idle stations disposed between each of the press stations to help in reorienting the part for subsequent processing. Although the idle stations may allow for shortening the transfer movements of the press, they also introduce a delay by adding extra stations. Additionally, the idle stations also require additional tooling. The idle stations add to the possibility of damaging the work piece by doubling the number of times the work piece is handled.
Therefore, a need has arisen for a system and method for transferring a work piece in a multi-station press that increases the speed at which large parts may be produced by the press, reduces the potential for damaged parts and allows for reorientation of a part between presses without significantly decreasing the speed of the press.